Vinyl aromatic monomer-conjugated diene monomer block copolymers (e.g., SBS: styrene-butadiene-styrene-block copolymer, SIS: styrene-isoprene-styrene-block copolymer) have been widely used recently as a base polymer for solution and hot-melt adhesives and viscous adhesives. For example, Patent Literature 1 and Patent Literature 2 disclose an adhesive composition or adhesive composition with an SBS. These adhesive compositions or adhesive compositions with an SBS or those with an SIS, however, have high melt viscosity and are insufficient in balance between melting characteristics or coatability and viscous adhesive characteristics such as tack strength.
For an improved solution over them, Patent Literature 3 discloses an adhesive composition containing a triblock copolymer and a diblock copolymer.
Patent Literature 4 discloses an adhesive composition containing a block copolymer obtained by coupling with a particular bifunctional coupling agent (an aliphatic monoester, a particular dihalogen compound).
Further, Patent Literature 5 discloses a composition containing: a block copolymer obtained by hydrogenating a block copolymer of a vinyl aromatic hydrocarbon compound and a conjugated diene compound at a particular percentage; and a tackifier.
Furthermore, Patent Literature 6 and Patent Literature 7 disclose an adhesive composition containing two or more block copolymer compositions for an improved solution.